18 Jun
2012
18 Jun
'12
1:58 p.m.
Hi Bruce,
I think I found the memory problem:
On Mon, Jun 18, 2012 at 7:07 PM, Bruce <Bruce at wild-hare.com> wrote:
I'm confused. ?The VC (Virtual Console) works okay
when you hit the reset
button, but when the computer is powered on you do not get the
OK
!000000
!
indication? ?(...per Chapter 5, Computer Self-Test, page 23)
Correct. On power on I only get an "O". VC does not respond at that
point. Once I hit the reset button, I do get
O000000
!
The VC then responds as expected.
If I remove the memory board, the behavior is exactly the same, except
that every memory address reads back as 177777 of course.
Accumulators with and without memory board:
without - 177777 125252 076000 000701
with - 127252 125252 076041 000701
This lead me to suspect that the memory at word 41 was incorrect.
Memory locations 0 - 40 were 052525, 41, 45, 51 were 127252, 42 and up
(except those with the lowest bits being 01) were 125252.
So, it looks like the entire memory is written with 125252
(1010101010101010) first, then each word is first read, then written
with 052525 (0101010101010101).
Sure enough, when I wrote 125252 to word 41, it looked fine, but when
I wrote 052525 to word 1, it changed word 41 to 127252!
So, it looks like the memory chip that controls bit 10 for addresses
ending in 01 (binary) is at fault here. I'm going to do some wire
tracing to find out which chip this might be...
The part numbers (005-xxxxxx-yy) are important when
trying to determine the
exact computer configuration as the same board may have different part
numbers depending upon what chips are stuff onto the board (i.e. memory
boards). ?If no 005 part number exists anywhere on the board the board
artwork 107-xxxxxx-yy number may be used in extreme situations. ?I do not
know of a 107 to 005 cross reference table but I could look at various
in-house boards if needed.
Like I wrote, the CPU and Memory board only have part of the label
left, it looks like the actual part numbers have carefully been
clipped off. All that remains are the "E" numbers, which I presume are
a serial number. The numbers on the boards themselves read:
CPU: 10700094903/0 07 (last 07 is printed, rest of the number is copper)
Mem: 10700081303/03 (entire number copper)
Also, the S/140, Nova 4/S, Nova 4/X could interchange
boards (CPU and
memory), so this system might not be a "true" Nova 4 - Eclipse boards could
be used rather than Nova boards if a Field Engineering guy didn't have the
"correct" parts. ?Nova/Eclipse CPU boards could be interchanged if the four
(4) PROM "personality" chips were swapped.
Could that be the reason the part numbers have been removed?
Although I don't think it's likely; all the PROM chips are soldered on
(no sockets), so swapping wouldn't be all that easy. Plus, the
soldering on the PROM chips looks like it's untouched.
There are a few other areas of the main board that do show evidence of
repairs; the following parts seem to have been replaced at some point
(with approx. board locations):
- One of the IDM2901A bit slices has been replaced with an AM2901BDC @ AE11
- 74S241 @ X13
- 74LS38 @ E45
- 4 75451 drivers around E22
Thanks,
Camiel.
19 Jun
19 Jun
1:40 a.m.
G'day Camiel -
The powerup microcode does a quick memory check, and the accumulator values
- 127252 125252 076041 000701
indicate that a '125252' was written to a 1K memory page whose last 10
bits were 041 (octal) but the data read back was '127252'.
The memory location '076041' indicates that the memory map was being
used to map a memory address using the "special address translation"
page of '076000'. This does not necessarily mean that location 000041
was bad, but some memory location whose last 10 address bits is 041.
(The special map page 31 (base address of 076000 when shifted left 10
bits) allows a programmer to address any physical memory location in 256
KW from within the logical address space of 32 KW.)
AC3's '000701' value is just an internal return location value that does
not point to any useful (to us) data (drat!).
FWI, the Nova 4X and S/140 power-on code does a
- test of memory pre-fetch processor
- test of MAP memory
- test of lower 16 KW memory
The error recovery for the 16 KW memory test is a "jmp ." (jump to self)
instruction which is why the "K" of the "OK" message never gets sent
to
the console.
Per Chapter 5 suggestions, does the memory board work in any of the
board slots, and does the memory bus terminator exist on the backplane?
Yes, sometimes FEs would "obfuscate" what boards were placed in client
machines during repairs so the client did not realize what was done to
repair the system - that is, to use Eclipse parts in a Nova. Othertimes
the labels just fell off the board. I'm sure there are many, many other
humorous possibilities.
The microcode PROM chips were indeed soldered on the boards, but there
was an underground business in the early 1980s unsoldering Nova 4/X
PROMs and substituting "non-approved(!)" Eclipse S/140 PROMs.
Without looking at the schematics, it would seem likely that I/O
buffer/driver chips you mentioned (i.e.74LS38, S241, 451) would be
subject to replacement over the years.
Bruce
On 6/18/2012 11:58 AM, Camiel Vanderhoeven wrote:
Hi Bruce,
I think I found the memory problem:
On Mon, Jun 18, 2012 at 7:07 PM, Bruce <Bruce at wild-hare.com> wrote:
I'm confused. The VC (Virtual Console) works
okay when you hit the reset
button, but when the computer is powered on you do not get the
OK
!000000
!
indication? (...per Chapter 5, Computer Self-Test, page 23)
Correct. On power on I only get an "O". VC does not respond at that
point. Once I hit the reset button, I do get
O000000
!
The VC then responds as expected.
If I remove the memory board, the behavior is exactly the same, except
that every memory address reads back as 177777 of course.
Accumulators with and without memory board:
without - 177777 125252 076000 000701
with - 127252 125252 076041 000701
This lead me to suspect that the memory at word 41 was incorrect.
Memory locations 0 - 40 were 052525, 41, 45, 51 were 127252, 42 and up
(except those with the lowest bits being 01) were 125252.
So, it looks like the entire memory is written with 125252
(1010101010101010) first, then each word is first read, then written
with 052525 (0101010101010101).
Sure enough, when I wrote 125252 to word 41, it looked fine, but when
I wrote 052525 to word 1, it changed word 41 to 127252!
So, it looks like the memory chip that controls bit 10 for addresses
ending in 01 (binary) is at fault here. I'm going to do some wire
tracing to find out which chip this might be...
The part numbers (005-xxxxxx-yy) are important
when trying to determine the
exact computer configuration as the same board may have different part
numbers depending upon what chips are stuff onto the board (i.e. memory
boards). If no 005 part number exists anywhere on the board the board
artwork 107-xxxxxx-yy number may be used in extreme situations. I do not
know of a 107 to 005 cross reference table but I could look at various
in-house boards if needed.
Like I wrote, the CPU and Memory board only have part of the label
left, it looks like the actual part numbers have carefully been
clipped off. All that remains are the "E" numbers, which I presume are
a serial number. The numbers on the boards themselves read:
CPU: 10700094903/0 07 (last 07 is printed, rest of the number is copper)
Mem: 10700081303/03 (entire number copper)
Also, the S/140, Nova 4/S, Nova 4/X could
interchange boards (CPU and
memory), so this system might not be a "true" Nova 4 - Eclipse boards could
be used rather than Nova boards if a Field Engineering guy didn't have the
"correct" parts. Nova/Eclipse CPU boards could be interchanged if the four
(4) PROM "personality" chips were swapped.
Could that be the reason the part numbers have been removed?
Although I don't think it's likely; all the PROM chips are soldered on
(no sockets), so swapping wouldn't be all that easy. Plus, the
soldering on the PROM chips looks like it's untouched.
There are a few other areas of the main board that do show evidence of
repairs; the following parts seem to have been replaced at some point
(with approx. board locations):
- One of the IDM2901A bit slices has been replaced with an AM2901BDC @ AE11
- 74S241 @ X13
- 74LS38 @ E45
- 4 75451 drivers around E22
Thanks,
Camiel.
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